1. Field of the Invention
The present invention relates to signal processing in an imaging apparatus, such as a digital camera and a video camera.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2003-107335 discusses an imaging apparatus that can detect a human face from a captured image (generally referred to as a face detection technique). The imaging apparatus can perform focusing processing, exposure control, and color correction with respect to a detected face region.
FIG. 7 is a timing chart showing an image capturing operation performed by a conventional imaging apparatus with the face detection technique. FIG. 8 is a flowchart showing the image capturing operation performed by the conventional imaging apparatus.
When a shutter release button is half pressed (i.e., when a switch SW1 is pressed), the imaging apparatus periodically captures an image of a photographic subject to display the image of the subject on an electronic viewfinder (hereinafter, referred to as an EVF), and generates an image signal. According to the NTSC method, the image signal can be generally updated at intervals of 1/30 second. When a power source of the imaging apparatus is turned on, the imaging apparatus can execute an image capturing operation starting with step S801.
In step S801, when the shutter release button is half pressed by a user (i.e., when the switch SW1 is pressed), the imaging apparatus performs an image capturing operation to obtain an image for face detection (step S802). In step S803, the imaging apparatus performs conventional face detection processing applied to the image signal captured in step S802.
Then, in step S804, the imaging apparatus obtains face information including skin color and face contour. In step S805, the imaging apparatus sets a photometry frame and a range-finding frame. Then, in step S806, the imaging apparatus performs an automatic exposure (referred to as “AE”) based on the information obtainable from the photometry frame set in step S805.
In step S807, the imaging apparatus performs automatic focusing (referred to as “AF”) processing for adjusting the focus position on the AF frame set in step S805. After the AF processing of step S807 is accomplished, the imaging apparatus causes a lamp (not shown) equipped in the apparatus body to emit an in-focus sign (step S808).
In step S809, when the shutter release button is fully pressed by the user (i.e., when a switch SW2 is turned on), the imaging apparatus starts a shooting operation (step S810). In step S811, the imaging apparatus performs predetermined signal processing, including white balance (“WB”) processing applied to a shot image including a human face being detected for optimizing color reproduction.
In step S812, the imaging apparatus converts an output signal in step S811 into a YUV signal. Then, the imaging apparatus compresses the YUV signal according to the JPEG compression method or a comparable compression method. In step S813, the imaging apparatus records the compressed signal into a CF (CompactFlash)® recording medium.
A conventional face detection module of an imaging apparatus includes the steps of scanning an image in response to turning-on of the switch SW1, performing face detection applied to the image, and then executing the AE and AF processing.
However, it is experimentally confirmed that a time required for the face detection module to detect a face is longer than the time required for the AF or AE processing even when a face detection algorithm is simplified.
Therefore, a shutter time lag (i.e., a time difference between ON timing of the switch SW1 and ON timing of the switch SW2) will be undesirably long.